1. The Field of the Invention
The present invention relates to flowable concrete mixtures and cured concrete obtained therefrom. More particularly, the present invention relates to concrete mixtures that have an aqueous based carbon encapsulating admixture.
2. Related Technology
Concrete mixtures are composite materials that are usually composed of water, cement, and aggregate. Common aggregates include sand, gravel, or crushed stone. Concrete is a well-known structural component with typical compressive strengths of about 2500 psi, when cured.
Admixtures are often added to concrete to give the concrete desired properties. Examples of suitable uses for concrete admixtures include lowering the concrete's density, improving the concrete's workability, improving the concrete's strength to weight ratio, giving the concrete insulating properties, and/or enhancing the acoustic properties of the concrete, among others. These beneficial properties are often accomplished by adding several different admixtures.
Air entraining agents are often used alone or in combination with other admixtures to give the concrete one or more of the foregoing properties. Air entraining admixtures are used to purposely trap microscopic air bubbles in the concrete. Air entrainment dramatically improves the durability of concrete exposed to moisture during cycles of freezing and thawing. In addition, entrained air greatly improves concrete's resistance to surface scaling caused by chemical deicers. Air entrainment also increases the workability of fresh concrete while eliminating or reducing segregation and bleeding.
There are several methods for entraining air in concrete. One approach is to generate bubbles or air pockets in situ. This approach can be accomplished using surfactants or other air entraining admixtures that generate bubbles as the concrete is mixed. Materials used to achieve these desired effects include non-ionic, cationic, and anionic surfactants, natural and synthetic resins, fatty acids, proteinaceous material, sulfonated hydrocarbons, and the like.
Another trend in concrete is to incorporate supplementary cementitious materials such as fly ash and pozzolans. However, many SCMs are known to reduce air entrainment and/or cause great variability in air entrainment, thereby making it difficult to achieve consistent results in the performance of the concrete (both wet and cured).
The desire to use SCMs such as fly ash in concrete is quite compelling due to cost reduction. There has been extensive research over a long period of time to mitigate the detrimental effects that fly ash and other SCMs can have on air entrainment. Despite this long felt need, there still does not exist a simple and economical solution to solve the variability in air entrainment when using fly ash.